Using game property to control actuator values (BGE Logic Bricks)
I don't think there is a way to achieve that with logic bricks but a small python script can. Simply paste this into a text block in blender's text editor and use the text block name in the python controller.

import bge
from mathutils import Vector

cont = bge.logic.getCurrentController()
own = cont.owner

sens = cont.sensors['Keyboard']
actu = cont.actuators['Motion']

actu.dRot = Vector((own['sp1'],0,0))

if sens.positive:
    cont.activate(actu)
else:
    cont.deactivate(actu)




The script should explain itself fairly well. By getting the controller object we can then get the owner and the sensor and actuator that we are interested in. We use the owner to access the game property own['sp1'] to alter the actuator values.

If you place the line print(type(actu)) you can find the type of actuator and lookup it's properties in blender's api reference. eg the simple motion actuator identifies as a KX_ObjectActuator

The last few lines activate or deactivate the motion actuator based on the output of the sensor.